Contact structure



June 11, 1940. J E -r CONTACT STRUCTURE Filed June 19, 1937 2 Sheets-Sheet 1 will...

" lNVENTOR JOHN-A.HERBST' BY H is W MTTOR Y June 11, 1940. J, A. HERBST cotmc'r STRUCTURE 2 Sheets-Sheet 2 Filed June 19, 1937 F l G INVENTOR JOHN A. HERBST 8Y7?z 7? 2 fiTORNZY Patented June 11, 1940 UNITED STATES PATENT OFFICE CONTACT STRUCTURE Application June 19, 1937, Serial No. 149,237

Claims.

This invention relates to electrical structure.

particularly adapted for vibratory contacts of high speed instruments such as relays employed in telegraph systems, telephone systems, auto- 5. matic stock quotation systems and the like.

Various attempts have been made heretofore to provide contacts for relays, interrupters and the like in which the formation of sparks or prolonged electric arcs between the contacts, which results in excessive erosion and burning of the contacts, is minimized or prevented, and various metals have been proposed, for example, platinum, alloys of platinum and iridium, tun sten carbide sintered with other metals acting as a binder for the tungsten carbide. Aside from the problem of reducing burning of the contacts, however, the problem of signal distortion due to contact bounce has been a serious one, particularly in high speed operating systems, for example, stock quotation systems. Any appreciable distortion of the signals in such systems tends to cause the stock quotation indicators, or other devices on which the quotations are displayed, to take incorrect settings, and the unfortunate results incident to the posting of a wrong stock price will readily be appreciated. Therefore, while it is highly desirable to prevent burning and pitting ofthe contacts thereby to obviate the necessity of unremitting attention and maintenance involving filing and burnishing of the contact faces, it is more important that correct, undistorted signals invariably will be transmitted or received by the relay contact structures employed in stock quotation transmitting, repeating and receiving st ations.

An object of the present invention is the provision of suitable means for eliminating chatter and bounce of contacts, thereby to obviate the foregoing disadvantages.

Another object of the present invention is the provision of a simple and effective contact structure wherein a critical adjustment of the contacts is not required.

Another object is the provision of comple- (Cl. zoo-nee) tion immediately following the closure of the contacts.

A still further object of the invention is the provision of a biasing field for a relay comprising two magnets so mounted that the flux of one magnet aids that of the other.

Still further objects will appear from a consideration of the description and drawings of a preferred embodiment of the invention, in which- Fig. l is a plan view of a relay employing the invention.

Fig. 2 is a view in elevation partly broken away of the relay of Fig. 1.

Fig. 3 is an enlarged view in elevation of the relay of Figs. 1 and 2 more clearly showing the electrical contact structure.

Fig. 4 is a view partly broken away taken along the line 4-4 of Fig, 1.

Figs. 5 to 10 show the action of the contacts as the relay of Fig. 1 operates.

Referring first to Figs. 1, 2 and 3 there is shown thereon a relay having two permanent magnets I and 2 secured thereto by means of the screws 3 and 4 in such a manner that the north pole of one magnet is directly above the north pole of the other when the relay is in the position shown in Fig. 2. The ends of the magnets are connected together by the strips 5 and 6 of magnetic material which support the pole pieces I and 8. The armature 9 moves laterally within the coil Ill and is provided with a resilient member l2 secured thereto by any suitable means, such as for example, by welding, the member l2 supporting a contact l3 preferably composed of an alloy of tungsten carbide, the surface characteristics of which contact are hereinafter set forth in detail. The armature 9 is normally in the position shown on Fig. 1 resting against the pole piece 8 but separated therefrom by a small disc l4 preferably of non-magnetic material to prevent a sticking action between the armature and the pole piece with the relay in the unoperated position. A similar disc is provided to engage the pole piece 1 when the relay is operated.

A resilient spring l5 secured by the screws 16 supports the contact I! and is tensioned against the adjusting screw I 8. The contacts l3 and I l are preferably provided with somewhat rounded contact surfaces although the surface of either contact may be fiat. The contact I! is insulated from the frame ll of the relay by the insulating Washers l9 and is provided with a terminal 2| to which is attached the conductor 22. Secured understood that when the contacts l3 and Il engage each other, a circuit is established by way of these contacts between the conductors 22 and 28 which terminate on slip connections or in any other suitable manner within the base 21 of the relay. The spring i5 has a resilient extension 24 supporting the contact, Fig. 4.

The limit of movement of the armature 9 is determined by the adjustment of the pole pieces l and 8, and the movement of the contact 13 is determined by the settings of the adjusting screws 25 and i8 and is such that the resilient member 42 normally rests against'the adjusting screw 25, and when the relay is in the operated position the armature 9 rests against pole piece 7 and the contacts i3 and ll are in engagement with each other. The pressure exerted by the contact i3 against the contact ll may be varied at will, by means of the adjusting screw IS, in accordance with the current flowing through these contacts.

The operation of the relay will best be understood by reference to Figs. 5 to 10 of the drawings, in which Fig. 5 shows the relay armature in the unoperated state with the armature 9 resting against the pole piece 8 but separated therefrom by the disc M. It will be understood that Figs. 5 to 10 are idealized for explanatory purposes, and are not to be taken as exact with respect to the extent of movement and fiexure of the contact springs, but are intended to illustrate the principles involved. To more clearly illustrate the action of the contacts, the make spring 24 is shown in the same plane as the armature spring H. As an impulse of the proper polarity is transmitted to the relay magnet coil, the armature 9 moves quickly toward the pole piece 1. The adjustment of the relay, however, is such that the contacts 13 and il engage each other before the armature comes into contact with the pole piece I as shown in Fig. 6. As the armature l4 continues its movement until it strikes the pole piece 1, the resilient armature member I2 is first flexed in the direction shown on Fig. 7 and the contact I3 moves relative to the contact 11. When the armature strikes the pole piece the armature contact continues to move in the direction of operation due to the inertia of motion stored up in it until the contacts assume the position shown in Fig. 8 and the contacts l3 and I1 have moved such that a second rubbing action betweeh the contacts l3 and I! has taken place, and the resilient spring 2 is flexed backward in the manner indicated. When the energy of inertia has been transferred from the armature contact to the make contact spring, the make contact spring 24 tends to restore thus transferring energy to the armature spring. When the energy has ben stored in the armature spring, a third rubbing action of the surfaces 01' the contacts has resulted and the contacts are in the position shown in Fig. 9.

A preferred contact material employed in connection with the present invention is an alloy of finely divided tungsten carbide sintered with an auxiliary metal such as iron, cobalt, nickel or osmium acting as a binder for the tungsten carbide. Several of such alloys are disclosed in the patent to Louis Casper, No. 2,056,919, issued October 6, 1936. When contacts comprising such material are closed, the heat generated by the current passing through the contacts melts some of the binder near the point of contact, thus releasing several particles of tungsten carbide. As

to the frame ii is a conductor 23 and it will be each particle is released it leaves a minute crater in the surface of the contact and thus causes the contact to have a rough surface during the life thereof. Therefore, when the two complementary contacts 13 and I1, composed of one of the above mentioned alloys of tungsten carbide, are closed, a frictional effect is obtained between the adjacent contact surfaces and, as hereinafter explained in detail, this frictional effect rapidly damps out the oscillations of the contact supporting springs.

The cycle of operations of Figs. 8 and 9 is repeated rapidly until all the energy has been dissipated at which time the contacts come to rest in the position shown in Fig. 10 with a slight fiexure in the springs i2 and 24. and with the contacts l3 and il in substantial alignment and exerting pressure against each other.

The rate of flexing of the springs I2 and 2| tends to follow their natural periods of vibration, and if the natural periods or frequencies, of the two springs were identical the contacts would tend to remain in contact closing position without chatter or bounce throughout the period of vibration of the springs;

However, it is impracticable to manufacture spring assemblies whose natural frequencies or periods of vibration are identical, and when metallic contacts having smooth surfaces are employed, as has heretofore been the practice, the back and forth movement of the contacts is repeated many times for each operation of the armature and this continued movement or vibration of the contact springs produces an out of phase relation between the contacts, causing the contacts to momentarily separate and distort the signal and also produce a spark or are at the contacts.

By employing tungsten carbide contacts having the surface characteristics herein described, and causing the frequencies of the contact supporting structures to be substantially the same, this oscillatory or vibratory condition of the contact springs is rapidly attenuated, and the contacts come to rest, after one or two such vibrations and before the phase diiference in frequencies of the armature and make contact springs has increased sufliciently to,produce a momentary separation of the contacts.

As the contact springs, flex in the manner described above, they produce motion of the contacts relative to one another in a direction normal to the line of operation which produces a rubbing action and frictional eflfect between the faces of the contacts. Since the contact faces are rough, considerable energy is required to overcome the friction between the contacts, and this energy is absorbed from the oscillatory motion of the contact springs, thus rapidly attenuating their vibration and bringing them quickly to rest.

The armature I4 is maintained in positive engagement with the pole piece 1 during the attenuation period by means of the flux set up by dual magnets I and 2 acting upon the flux set up in the armature l by the current in the electromagnet II, and this action of the dual magnets also assists in preventing contact bounce. This will he more clearly understood from the following consideration of the pull exerted on the armature 9 by the magnetic fields set up in the relay. Where x represents the value of flux which is normally set up because of the presence of the permanent magnets I and 2, and Y represents the flux set up by the current passing through the electromagnet H), the effective pull on the armature when the relay is energized may be determined generally by the expression The component of the total flux which is effective to actuate the armature 9 and to hold it in its actuated position is represented by the second term 2XY. Therefore, by using ,dual magnets, the value of X is large, and the product represented by the term 2XY is correspondingly large, which causes quick response of the armature and positive action in maintaining the armature in its actuated position. In other words, the force which actuates the armature is proportional to the product of the permanent flux and the flux generated by the electromagnet I0, and since the flux set up by the dual magnets produces a very high flux density at the pole pieces, the strength of which flux is a factor in the action of the relay, the relay not only has an improved and positive action, but the force tending to hold the contacts together is much greater for a given current, thereby tending to prevent vibration and separation of the contacts when they are in circuit closing position. It will be understood that the sign plus or minus before the term 2XY is determined by the direction of the current flowing in the electromagnet In, the armature 9 moving to circuit closing position in response to current of proper polarity.

While the invention has been described in detail with respect to a particular preferred example thereof which gives satisfactory results, it will be understood by those skilled in the art after understanding the invention, that various changes, substitutions and modifications may be made without departing from the spirit and scope of the invention, and it is intended therefore in the appended claims to cover all such changes and modifications. As heretofore stated, the contact material preferably is composed of or comprises an alloy of tungsten carbide, but obviously any other alloy or metallic substance which will maintain a sufficiently rough surface to give the stated frictional effects, and which has the necessary electrical characteristics, may be employed.

What is claimed as new desired to be secured by Letters Patent is:

1. An electrical switch structure comprising at least two complementary metallic contact members, mounting means whereby said contact members are movable towards and from each other for controlling-the flow of current in an electrical circuit, said mounting means causing a wiping action between the contact members as they are moved into circuit closing position, at least one of said contact members comprising a finely divided metallic compound sintered with a metal binder which, when current passes through said contact member, melts sufficiently to release particles of the finely divided metallic compound at the point of contact and leave minute craters in the surface of the contact member thereby to cause the member to have and retain a hard, rough contact surface in operation, said rough contact surface and said wiping action causing frictional effects to damp the vibrations of said contact members and prevent contact bounce.

2. A relay comprising a plurality of contacts for controlling the flow of current in an electrical circuit, said contacts comprising tungsten carbide sintered with a metal binder which, when the current passes through said contacts, melts sufficiently to release particles of the tungsten carbide and cause the contacts to have and retain hard, rough faces in operation, and means including yieldable supports for said contacts having substantially the same period of vibration, said contacts and supports coacting, when the contacts are brought into electrical engagement with one another, to cause movement of the contacts relative to each other in such time relation as to prevent separation of the contacts during said movement and to bring the contacts quickly to rest by reason of the friction between the rough surfaces thereof.

3. A relay structure including resilent contact mounting means, a pair of metallic contacts supported by said means for controlling the flow of current in an electrical circuit, said contacts comprising tungsten carbide sintered with a metal binder which, when the current passes through said contacts, melts sufiiciently to release particles of the tungsten carbide and cause the contacts to have and retain rough contact faces in operation, said rough contact faces coacting to prevent any phase difference in the frequencies of the resilient mounting means from causing a momentary separation of said contacts as the relay is operated to circuit closing position.

4. An electrical contact structure including a plurality of metallic contact elements for controlling the flow of current in an electrical circuit, said contacts comprising tungsten carbide sintered with a metal binder which, when the current passes through said contacts, melts sufficiently to release particles of the tungsten carbide and cause the contacts to have and retain hard, rough faces in operation, a resilient mounting for each of said contact elements, said mountings having substantially the same frequency, and means including said hard rough faces and said mountings for causing the contact elements to remain in continuous contact during the operating period of said elements.

5. An electrical contact structure comprising a plurality of complementary metallic contact members, at least one of which members comprising tungsten carbide sintered with a metal binder which, when the current passes through said member, melts sufficiently to release particles of the tungsten carbide and cause the member to have and retain a hard, rough contact surface in operation, and mounting means whereby one of said contacts is movable relative to the other, said mounting means causing a wiping action between the contacts as the contacts are brought into circuit closing position, said rough contact surface and said wiping action causing frictional effects to damp the vibrations of said contact members and prevent contact bounce.

JOHN A. HERBST. 

